Field of the Invention
The invention relates to a configuration for transmitting light between two locations having different electric potentials. The invention further relates to a method of producing a configuration for transmitting light between two locations having different electric potentials.
In order to measure physical variables, such as electric current or electric voltage, for example, at a high voltage potential, the measured signals must be transmitted from sensors provided in order to measure the variables in a manner that is at a potential separated from earth potential. Potential-free transmission of the measured signals is possible, as is known, in the form of optical signals via optical waveguides, which are led from the high voltage potential to earth potential. Systems are also known in which, in addition to the measured signals, the power for the sensors that are located on the high voltage side is also transmitted optically via optical waveguides.
The optical waveguides have to be protected against mechanical stresses. Furthermore, for the electrical insulation, a sufficiently high electrical breakdown gap and generally also a sufficiently high electrical creep path between the high voltage side and the earth potential side must be ensured.
European Patent EP 0 265 737 B1 discloses a configuration for transmitting the measured signals of a current transformer at a high voltage potential to earth potential in the form of optical signals. The known configuration includes a tubular high voltage insulator running vertically from a current transformer to a base that is lying at earth potential. The insulator is made of ceramic or glass-fiber reinforced plastic (GRP), and one or more optical conductors in an optical conductor cable, which is led in a helix through an internal space of the high voltage insulator. The optical measured signals are transmitted via the optical conductors. The internal space of the high voltage insulator can be filled with air or with an insulating gas, such as nitrogen (N.sub.2) or sulphur hexafluoride (SF.sub.6). In another embodiment of this known configuration, the optical conductor cable is wound externally in a helix onto the insulator tube and embedded in a cast-on silicon layer or even completely covered by the silicon layer. In addition, silicon sheds to lengthen the surface creep path are formed with the silicon layer. In the case of the configuration disclosed by European Patent EP 0 265 737 B1, in the embodiment with insulating gas, the insulating gas must be refilled in the case of leaks, for example during mounting operations. In the case of the embedding of the optical conductor cable in silicon, problems may arise at the interface between the silicon and the optical conductor cable, as a result of thermal volume changes of the silicon during temperature changes. The volume changes can lead to longitudinal gaps in the silicon along the optical conductor cable, into which gaps moisture can penetrate. This can result in creeping discharges.